SMBus Fan Control with 1°C Accurate Temperature Monitoring
Datasheet
Chapter 4 System Management Bus Interface Protocol
4.1
System Management Bus Interface Protocol
The EMC2101 communicates with a host controller, such as an SMSC SIO, through the SMBus. The
SMBus is a two-wire serial communication protocol between a computer host and its peripheral
devices. A detailed timing diagram is shown in Figure 4.1. Stretching of the SMCLK signal is supported,
however the EMC2101 will not stretch the clock signal.
The EMC2101 powers up as an SMBus client (after loading from EEPROM as applicable).
TLOW
THIGH
THD:STA
TSU:STO
TRISE
TFALL
SMCLK
TSU:STA
THD:STA
THD:DAT
TSU:DAT
SMDTA
TBUF
S
S
P
P - Stop Condition
P
S - Start Condition
Figure 4.1 SMBus Timing Diagram
The EMC2101 is SMBus 2.0 compatible and supports Send Byte, Read Byte, Receive Byte and the
Alert Response Address as valid protocols as shown below.
All of the below protocols use the convention in Table 4.1.
Table 4.1 Protocol Format
DATA SENT
TO DEVICE
DATA SENT TO
THE HOST
# of bits sent
# of bits sent
4.2
Write Byte
The Write Byte is used to write one byte of data to the registers as shown below Table 4.2:
Table 4.2 Write Byte Protocol
SLAVE
ADDRESS
REGISTER
ADDRESS
REGISTER
DATA
START
WR
ACK
ACK
ACK
STOP
1
7
1
1
8
1
8
1
1
Revision 2.53 (03-13-07)
SMSC EMC2101
DATA1S4HEET
SMSC [ SMSC CORPORATION ]
